This invention relates generally to gyroplane rotary wing aircraft, also known as autogyros, and more particularly to a system of collective blade pitch adjustment for use on teter-bar type gyroplane rotors.
Gyroplane rotary wing aircraft, historically called autogyros, have flown with various types of rotors and rotor hubs. In order to fly successfully, all gyroplanes must incorporate certain essential features in their rotors. Gyroplane rotors, the rotary wings which keep the aircraft aloft, are rotated by air currents, not by engine torque, as with helicopters. A propeller pushes or pulls the gyroplane through the air like an airplane, and the air currents cause the rotor to turn by a process called autorotation. As the rotating blades pass through the air during forward flight, the blades on one side of the rotor are advancing, producing higher relative air speed, as compared with the retreating blades on the other side of the rotor. To compensate for differences in the lift between the advancing and retreating blades, all gyroplane rotors include some means to permit the rotor blades to "flap," or move up and down as they circle the rotor hub. The flapping of the blades equalizes the lift and permits the gyroplane to move laterally through the air in stable flight. The need to provide for rotor blade flap, as well as other articulations inc ertain gyroplane designs, has led to various types and configurations of rotors and rotor hubs. By the end of the first phase of gyroplane (autogyro) design, in the 1940s, relatively complex rotors and hubs were in use. Such rotors, generally called fully articulated rotors, are similar to helicopter rotors. To these relatively complex, fully articulated rotors, collective pitch control was eventually added. Collective pitch control is a system for chainging the pitch of all the rotor blades simultaniously. Collective pitch control allows the gyroplane to perform a jump take-off, using a mechanical pre-spin system for turning the rotor. A jump take-off is achieved by spinning the rotor rapidly with the rotor blades de-pitched, and then adding positive pitch to all blades simultaneously, producing instant vertical lift. The jump take-off was an important advance for gyroplanes, but it was only achieved with relatively complex to operate mechanisms which were also mechanically complex. Even with jump take-off, the gyroplane could not compete with the helicopter, which quickly captured the market for rotary wing aircraft.
An important area of focus in recent years has been the design of simple ultralight gyroplanes which usually seat just one person. These gyroplanes use simple two-blade rotors and avoid the complex fully articulated hubs of earlier multi-blade designs. Since the new, simpler gyroplanes must contend with the same physical forces as their more complex predecessors, some form of blade articulation still must be provided. The solution employed in simple, modern gyroplanes is what is termed a "teter-bar" blade mounting; also known as a "see-saw type" blade mounting. In such a rotor, a teter-bar is mounted, underslung, between upright plates, with a blade attached to each end of the teter-bar. The plates, teter-bar and blades all turn on a hub. Such a rotor system is commonly termed "semi-rigid," since it retains the flap motion but forces the blades to move together, in a see-saw fashion. Teter-bar rotors are simple and effective and it would be advantageous to be able to incorporate a means for producing a collective pitch change in such rotors to permit jump takeoffs. It would also be advantageous to provide a system for collective pitch change in a teter-bar rotor which is both simple and rugged.